1. Field of the Invention
The present invention relates to grease for a rolling bearing and a grease-sealed rolling bearing which is used under severe conditions such as high temperature, high-speed rotation and high load.
2. Prior Art
In rolling bearings used around automobile engines and the like which operate at high temperatures, high rotations and high loads, their lives have been shorter than the theoretical lives due to increased severe operating conditions such as higher temperatures, higher-speed rotations and higher loads in recent years.
Recent studies have shown that the above disadvantage is not caused by the life of grease being sealed in the rolling bearing but the rolling bearing itself. Specifically, a large force in the tangential direction which accompanies slip is produced between a surface of a rolling element and a raceway surface of inner and outer bearing rings during high-speed rotation, leading to the fatigue life in early stages.
In order to reduce the force in the tangential direction which is exerted on the rolling bearings, there have been attempts to select a suitable lubricating base oil used in grease which meets the operating conditions and can exhibit optimum lubricity under high temperature and high speed rotation conditions. However, it has been difficult to satisfactorily comply with more severe operating conditions merely by selecting lubricating base oil.
An object of the present invention is to provide grease for a rolling bearing, which can prevent a rolling bearing used under particularly severe conditions from leading to the fatigue life in the early stages, to lengthen the life of the rolling bearing.
Another object of the present invention is to provide a grease-sealed rolling bearing having long life, which does not lead to the fatigue life in the early stages, even under severe conditions.
The present invention is directed to:
(A) grease for a rolling bearing used under severe conditions such as high temperature, high-speed rotation and high road, comprising (i) a lubricating base oil containing at least a poly-xcex1-olefin synthetic oil or a diphenyl ether synthetic oil, (ii) a diurea thickening agent of the general formula: 
xe2x80x83wherein R2 is a diisocyanate residue, and R1 and R3 are amine residues, and (iii) a compound selected from the group consisting of an organic antimony compound and an organic molybdenum compound which can form reacted films with a metal composing inner and outer bearing rings and a rolling element of said rolling bearing on a raceway surface of said bearing rings and a surface of said rolling element; and
(B) a grease-sealed rolling bearing in which the above grease for a rolling bearing is sealed.
In the grease for a rolling bearing and the grease-sealed rolling bearing, an organic antimony compound such as antimony dithiocarbamate or an organic molybdenum compound such as molybdenum dithiocarbamate, which have been contained as an anti-wear agent in the grease, reacts with a metal composing inner and outer bearing rings and a rolling element at high temperatures. For example, it is over 200xc2x0 C. on the rolling contact areas in rolling bearings used in automobile engines. As a result, there are formed reacted films which can contribute to the reduction of the force in the tangential direction on a raceway surface of the bearing rings and a surface of the rolling element, thereby preventing the production of large force in the tangential direction at high-speed rotations.
By the poly-xcex1-olefin synthetic oil or the diphenyl ether synthetic oil as lubricating base oil, and the diurea thickening agent of the general formula (1), optimum characteristics of the organic antimony compound or the organic molybdenum compound can be achieved. They also function to compose grease having lubricity most suited to the operating conditions of the rolling bearing.
Thus in the present invention, it is possible to lengthen the rolling bearing life by preventing the rolling bearing used under particularly severe conditions from leading to the fatigue life in the early stages.